Carbon dioxide cleaning
Carbon dioxide cleaning (CO2 cleaning) comprises a family of methods for
Applications
CO2 cleaning has found application in many industries and technical areas, including aerospace, automotive, electronics, medical, manufacturing, basic and applied research, and
Methods
Carbon dioxide cleaning refers to several different methods for parts cleaning, making use of all phases of CO2:[7] basic methods include solid dry ice pellets, liquid CO2, CO2 snow (a hybrid method), and supercritical CO2. The different forms of CO2 cleaning can clean many types of objects, from large generators to small and delicate parts, including hard drives and optics.[4]: 270
Pellets
In pellet cleaning ("dry-ice blasting"), relatively large pellets of solid CO2 are fired at the surface to be cleaned. These pellets impinge on the surface, mechanically dislodging contaminant particles. Pellet cleaning is only appropriate for surfaces sturdy enough to withstand significant impacts.[1][4]: 276
Snow cleaning
In CO2 snow cleaning, compressed liquid or gaseous carbon dioxide is expelled from a nozzle, condensing into a mixture of solid particles and gas, which impact the surface to be cleaned.[1][4]: 276 Jet velocities are frequently supersonic.[8] Snow cleaning works by a combination of momentum transfer (mechanically dislodging contaminant particles) and solvent action.[1][4]: 273 The CO2 sublimates on contact, increasing in volume up to 800 times, thereby generating pressure to sweep particles away.[8] The CO2 also dissolves hydrocarbon contaminants, and its low temperature embrittles residues such as fingerprints, making them easier to blow away.[2][9]
Snow cleaning has found application in the
Equipment costs for a carbon dioxide snow cleaning system can range from US$1500 for a basic system to $50,000 for a high-end automated unit.[4]: 292 Material costs are comparatively low, although ultra-pure CO2 must often be used to avoid the introduction of new contaminants.
Supercritical fluid
At temperatures and pressures above its critical point, CO2 can be maintained as a supercritical fluid, exhibiting extremely low viscosity and high solvency. To apply this method, parts to be cleaned are enclosed in a pressure vessel that is then filled with supercritical CO2. This method is appropriate for small and delicate parts such as microelectronics, and is not ideal for particulate removal.[12][1] Aside from cleaning, applications of supercritical carbon dioxide include targeted chemical supercritical fluid extraction and materials processing.
Liquid CO2 washing
Liquid CO2 washing, like supercritical fluid CO2 washing, relies on the high solvent power of CO2,[4]: 275 but at lower temperatures and pressures, the latter making it simpler to implement. Because liquid CO2 does not have the solvent power of the supercritical fluid, agitation and surfactants may be added to improve the effectiveness of the method.[1] Liquid CO2 has been used in dry cleaning and machined parts degreasing.
History
Carbon dioxide cleaning was contemplated in the 1930s, and the "pellet" approach was developed in the 1970s by E.E. Rice, C.H. Franklin, and C.C. Wong.[4]: 276
The introduction of CO2 snow cleaning, with its ability to remove sub-micron-scale particles, is credited to Stuart Hoenig of the
Nozzle design is the most significant factor in carbon dioxide snow cleaning performance, affecting the size and velocity of the dry ice particles.[4]: 277–278 Variations in nozzle design have been developed by W.H. Whitlock, L.L. Layden, Applied Surface Technologies, and Sierra Systems Group.[4]: 277
Issues
Safety
CO2 cleaning may present certain safety risks. If the process is used to remove hazardous materials, precautions must be taken to avoid exposure to these materials in the vent stream. Because the CO2 stream is
Contamination
Some commercial grades of carbon dioxide may contain traces of heavy
: 292–294Static charge
References
- ^ a b c d e f "Cleaning Methods". Carbon Dioxide Snow Cleaning. Applied Surface Technologies. Retrieved 13 August 2015.
- ^ a b c "About Us". Carbon Dioxide Snow Cleaning. Applied Surface Technologies. Retrieved 4 August 2015.
- ^ "What is Dry Ice Blasting (Cleaning)?". Cold Jet. Retrieved 23 September 2015.
- ^ a b c d e f g h i j k l m n o p q r Sherman, Robert; Adams, Paul (1995). "Carbon Dioxide Snow Cleaning – The Next Generation of Clean" (PDF). Precision Cleaning: 271–300. Retrieved 24 September 2015.
- ^ a b "Applications". Carbon Dioxide Snow Cleaning. Applied Surface Technologies. Retrieved 23 September 2015.
- ^ a b "Industries and applications". Cold Jet. Retrieved 23 September 2015.
- ^ "co2clean". co2clean. Retrieved 2016-05-24.
- ^ a b "How does CO2 Blasting Work?". Cold Jet. Retrieved 23 September 2015.
- ^ a b c "Space probes: sterile launch into outer space". Phys Org. Fraunhofer-Gesellschaft. August 3, 2015. Retrieved 4 August 2015.
- ^ "AFM". Carbon Dioxide Snow Cleaning. Applied Surface Technologies. Retrieved 24 May 2016.
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- ^ A US 5125979 A, Swain, Eugene A.; Carter, Stephen R. & Hoenig, Stuart A., "Carbon dioxide snow agglomeration and acceleration", published Jun 30, 1992
- ^ "FAQ". Carbon Dioxide Snow Cleaning. Applied Surface Technologies. Retrieved 23 September 2015.
- ^ "Safety Issues". Carbon Dioxide Snow Cleaning. Applied Surface Technologies. Retrieved 23 September 2015.